The present invention relates generally to locks and more particularly to a padlock with an alarm which sounds when someone tries to violate or tamper with the padlock.
Generally, a padlock comprises a body and a shackle having a pair of legs. The shackle is mounted for reciprocal movement relative to the body between a closed first position and an open second position. Located within the body is a latch for engaging one leg of the shackle when the shackle is in its closed position, and this prevents movement of the shackle to its open position. In order to move the shackle from its closed to its open position, the latch must be disengaged, and the padlock includes a lock mechanism operable to disengage the latch. The lock mechanism may be key operated or combination-operated in an authorized manner. The padlock is typically composed of a hard metal such as steel.
Padlocks are used for securing possessions or property to prevent theft or trespassing. It is not uncommon, however, for someone intent on theft or trespassing to tamper with the padlock in an attempt to open it in an unauthorized manner, either by severing the shackle or by forcing it into an open position. To deter a thief or the like from tampering with the padlock, it has been proposed to provide the padlock with an integral alarm system which sounds an alarm when the thief violates or tampers with the padlock. A padlock having an integral alarm system is disclosed in Stevens, U.S. Pat. No. 3,993,987. Such a system conventionally includes, in addition to the alarm sounding device, a battery for energizing the alarm sounding device and an electrical circuit and switches connecting the alarm sounding device to the battery and causing the alarm sounding device to operate when a violation occurs or an attempt is made to tamper with the padlock.
Because such an alarm system is powered by a battery, and because a battery can wear out, it is desirable to be able to test the battery to determine whether it still has sufficient power to operate the alarm. Provision for testing the battery is made in the system disclosed in the above-noted Stevens patent, but the test is complicated. First the lock mechanism must be opened with a key to open the shackle and then the lock mechanism must be closed with a key while the shackle is in its open position. Moreover, to shut off an alarm undergoing testing, either the lock mechanism must then be opened with a key or the shackle must be closed. No provision is made for automatic testing of the alarm so that, should one forget to proceed through the manipulative steps required in order to test the battery in the Stevens system, the battery could wear out without one knowing it. Furthermore, if the shackle is opened with a key, and the key is then removed, the Stevens alarm will sound, which is bothersome and otherwise undesirable.
Moreover, because all batteries eventually wear out and must be replaced, access must be provided to the battery within the padlock to permit removal and replacement of the battery. Such a provision, however, gives a thief the opportunity to gain access to the battery to remove it and deactivate the alarm. In Stevens there is no provision for sounding the alarm when a thief gains access to the battery.